[U-Boot] [PATCH] pci: Support parsing PCI controller DT subnodes

[Marek Vasut]

On 09/03/2018 01:35 AM, Simon Glass wrote:
> Hi Marek,
> 
> On 2 September 2018 at 12:24, Marek Vasut <marek.vasut at gmail.com> wrote:
>> On 09/02/2018 03:07 AM, Simon Glass wrote:
>>> Hi Marek,
>>>
>>> On 1 September 2018 at 16:43, Marek Vasut <marek.vasut at gmail.com> wrote:
>>>> On 09/01/2018 11:45 PM, Simon Glass wrote:
>>>>> Hi Marek,
>>>>>
>>>>> On 30 August 2018 at 03:25, Marek Vasut <marek.vasut at gmail.com> wrote:
>>>>>>
>>>>>> On 08/30/2018 02:29 AM, Simon Glass wrote:
>>>>>>> Hi Marek,
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>>>>> If you have both EHCI and a xHCI controller which can occupy the same
>>>>>>>>> BFD, then how would you supply in the DT options needed by the
>>>>>>>>> controller itself? Don't you need two nodes in that case?
>>>>>>>>
>>>>>>>> For the PHY case, it's controller-type-independent.
>>>>>>>
>>>>>>> What do you mean? Your example of why you can't use compatible strings
>>>>>>> says you might have two different PHYs. But I think you should answer
>>>>>>> my questions:
>>>>>>>
>>>>>>>>> If you have both EHCI and a xHCI controller which can occupy the same
>>>>>>>>> BFD, then how would you supply in the DT options needed by the
>>>>>>>>> controller itself? Don't you need two nodes in that case?
>>>>>>
>>>>>> You need only one node (if the PHY works with both controller options),
>>>>>> which contains "reg" and "phy" properties. The driver matching is done
>>>>>> on the PCI ID/class and the node is associated with the driver based on
>>>>>> the "reg" property.
>>>>>
>>>>> I think you need two nodes if there are DT options that are different
>>>>> for each PHY. In fact I think this is impossible to do with the reg
>>>>> scheme.
>>>>>
>>>>> In effect the PHYs are different. They have different drivers,
>>>>> assuming drivers are needed. So I feel that using a common address to
>>>>> match two different devices is actually just weird.
>>>>
>>>> I think I lost you. But this discussion is really hypothetical. You
>>>> _can_ have a USB PHY which can attach to both USB 2 and USB 3
>>>> controller, in which case you would have only one DT node to describe it.
>>>
>>> Can you point to an example of this? Otherwise it seems hypothetical.
>>
>> Nope, it's just electrically viable.
> 
> OK, well I'm not sure that we can make any claims about any of this
> unless it is used somewhere.
> 
>>
>>> As a counter-example, see exynos54xx.dtsi.
>>
>> What exactly am I looking for ?
> 
> You can see a USB3 PHY which is attached to a USB3 host.
> 
>>
>>> I believe the correct way to do this is to enable/disable DT nodes. Do
>>> you have any pointers to suggest that the same node should be used for
>>> two devices?
>>
>> Nope
> 
> Then I believe that is incorrect, and it should be handled using two
> separate notes, with only one enabled at run-time.

I don't think you can claim it's either correct or incorrect if there is
no such hardware.

-- 
Best regards,
Marek Vasut